Physico-chemical Properties

Hydrogen peroxide (H2O2) is a colorless water-soluble liquid. The molecule of hydrogen peroxide is asymmetrical and strongly polarized. A high tendency to form hydrogen-bond networks causes higher viscosity than water. Because of free electron pairs on both oxygen atoms, the H2O2-molecule tends to form donor-acceptor compounds. Pure hydrogen peroxide is primarily of scientific interest only. Its aqueous solutions, however, are widely used in many industrial branches for various applications. Important physical properties of hydrogen peroxide and its aqueous solutions as summarized in the table on the left side.

The molecular structure as well as oxygen's oxidation state define the chemical properties of hydrogen peroxide. The oxygen atom, being in the oxidation state I, allows hydrogen peroxide to participate in both oxidation as well as reduction reactions. Although hydrogen peroxide is well known as a strong oxidizing agent, its reduction properties play an important role in some applications. Typical chemical reactions, in which hydrogen peroxide is involved, are oxidation and reduction reactions, formations of other peroxygen or adduct compounds. In contrast to many other redox agents, hydrogen peroxide introduces no additional substances other than water into the reaction system and an excess can be easily decomposed into water and oxygen, not interfering thereby with subsequent reaction steps. Hydrogen peroxide is often regarded as a true "green chemical".

Despite its high reactivity, pure hydrogen peroxide is a stable substance and, if kept under optimal conditions, can be stored for years. The most important factors increasing the rate of decomposition are high pH value, high temperatures, UV-irradiation, presence of transition metal salts and all kinds of impurities.

The decomposition of hydrogen peroxide into oxygen and water is a quite complex process, which involves formation of various free radicals. In some applications (soil remediation) the induced instability is intentionally caused and used.

Important physico-chemical properties of aqueous solutions of hydrogen peroxide

H2O2 concentration*

%(wt.)

0

30

35

50

60

70

100

g(H2O2)/kg

300

350

500

600

700

g(H2O2)/l

332

395

596

742

899

mol/l 

9,8

11,6

17,5

21,8

26,4

mol% 

18,5

22,2

34,6

44,3

55,3

Active oxygen content 

%(wt.) 

0

14,1

16,5

23,5

28,2

32,9

47,1

Molecular weight

g/mol 

18,015

34,015

Density at 20 °C 

g/ml 

0,998

1,111

1,131

1,195

1,241

1,289

1,450

Freezing point 

°C

0

-26

-33

-52

-56

-40

-0,4

Boiling point at 1013 mbar. 

°C 

100

106

108

114

119

125

150

Boiling point at 2026 mbar. 

°C 

132

135

145

152

158

Boiling point at 3039 mbar. 

°C 

147

150

161

168

176

Total vapor pressure (30 °C) 

mbar

42

33

32

14

19

15

8

mm. Hg.

31,6

25

24

18

14

11

6

H₂O₂ partial vapor 

mbar

0,3

0,4

0,8

1,2

1,7

pressure at 30 °C 

mm. Hg. 

0,25

0,3

0,6

0,9

1,3

Specific heat at 25°C 

J*g/K 

4,2

3,6

3,5

3,3

3,2

3,1

2,6

Refractive index,
n25D at 25°C

1,3325

1,3519

1,3554

1,3661

1,3734

1,3814

1,4067

Viscosity at 20°C 

mPa*s 

1,00

1,11

1,12

1,18

1,21

1,23

1,25

Surface tension at 20°C 

mN/m 

72,8

74,2

74,5

75,7

76,4

77,3

80,4

The tabulated values, which are given above, describe physico-chemical properties of salt free pure aqueous solutions of hydrogen peroxide in water. 

*Hydrogen peroxide concentration can be expressed in weight percent, gram of 100%-age hydrogen peroxide in 1 kg solution, gram of 100%-age hydrogen peroxide in 1L solution and as molar concentration or molar fraction of hydrogen peroxide in solution. The tabulated values for g(H2O2)/l and mol/l are given for the temperature of 25 °C.